There have been a number of proposals for providing bypass or circulating valves for use in oil wells. For example, U.S. Pat. No. 3,500,911 discloses a device which has an internally mounted valve sleeve 50 which opens and uncovers the port 64 while the string is being run to the depth of the formation in response to the hydrostatic pressure of the well fluid. The valve 50 closes when the pressure reaches a certain minimum value and is for use with packers for open hole drill stem testing of wells.
U.S. Pat. No. 3,542,130 discloses a valve for removing paraffin from oil wells in which there is a spring loaded sleeve with a restriction in the sleeve that is used to hold a wax plug to close off the sleeve allowing it to move downwardly so that hot oil may pass out through the port 68. The hot oil dissolves wax in the string and flows back up through the pipe and carries the then melted wax plug along with the paraffin in the well to the surface.
U.S. Pat. No. 4,049,057 discloses a paraffin cleaner in which there are valves in a unit, which does have an unrestricted passage through it but the unit is eccentrically mounted, utilizes cupped or Belville washers, and does not circulate treating fluid out of the cleaner about a circumference of 360.degree..
U.S. Pat. No. 3,376,936 discloses a bypass for removing paraffin in which a sliding sleeve arrangement is operated from the surface to uncover ports to allow the hot oil to pass out of the oil string.
None of the foregoing patents, however, discloses a pressure differential circulating valve which becomes an integral part of the tubing string, is of small enough external diameter so that it can be readily disposed in a normal casing string in the well bore and yet have an unrestricted passageway through it of substantially the same size and shape as the tubing string, which can be set to open at any desired pressure, and which is opened by applying flow pressure to the tubing, such as from the surface, so that fluid, such as hot oil or other treating fluid, can circulate down through the tubing and out 360.degree. through the pressure differential circulating valve, and when the treatment is completed, the pressure differential circulating valve automatically closes for resumption of normal operations, such as pumping oil by sucker rods extending through the passageways in the tubing and in the pressure differential circulating tool to the surface.